Wireless communication systems, for example, cellular radiotelephone systems, are well known. These systems provide communication services utilizing radio frequency transmission techniques between land based radio transceiver stations, or base stations, and mobile radio transceivers, or mobiles. Each of the base stations and the mobiles thus include a radio transceiver for communicating voice, data, or other information utilizing a communication resource, i.e., a radio link, and a standard communication protocol. For example, several such protocols for cellular radiotelephony are the Narrowband Advanced Mobile Phone System (NAMPS), the Advanced Mobile Phone System (AMPS), the Global System for Mobile Communications (GSM), the Personal Communication System (PCS), the United States Digital Cellular (USDC), or the Code Division Multiple Access (CDMA) protocols.
A common feature of these wireless communication systems is that a large geographic area is divided into smaller areas ("cells"), which are serviced by a base station. The use of cells to subdivide the large geographic area permits enhanced geographic coverage with efficient use of radio frequency resources. For example, radio frequency resources assigned to one cell may be reused in cells located a sufficient distance from this cell without the resources interfering. During the design and implementation of a cellular communication system, careful planning is undertaken to assign communication resources to cells to ensure sufficient capacity, i.e., to assign a sufficient number of resources to handle the anticipated number of calls at a given time within the cell, and to ensure that communication resources assigned to one cell do not cause unacceptable levels of interference in adjacent or neighboring cells.
The ever increasing popularity of cellular systems with their users has created a need to increase system capacity. An advantage of the cellular system in providing greater capacity is that cell sizes may be reduced, by limiting the transmission power of the base stations and mobiles, permitting increased reuse of communication resources. Greater reuse of communication resources in a given geographic area equates to increased capacity.
One type of cellular system utilizing particularly small cell sizes is referred to as a "picocellular" system including very small geographic sized "picocells." Picocellular systems find particularly advantageous use as in-building cellular radiotelephone systems. Implementing wireless communications systems within a building poses numerous problems because of the building topology. The picocellular systems require a high degree of optimization to successfully interact with the surrounding "macrocellular" environment, as well as to provide the highest quality of service to the in-building users. Perhaps the largest optimization effort is due to the installation of the many required base stations, one each for each picocell. Each picocell requires assignment of a broadcast carrier including a broadcast control channel for supplying "coverage" in the picocell, and the assignment of traffic carriers for handling the call traffic within the cells. The broadcast control channel is utilized by the base station and the mobiles to request and establish service, i.e., to make and complete calls. Once service is established, the mobile is assigned a traffic channel resource on which the call is conducted.
The broadcast control channel is referred to as a dedicated channel. That is, its signal characteristics, e.g., carrier, transmission power, timing, etc., are necessarily fixed. However, fixing certain characteristics of the broadcast control channel, i.e., its carrier and power, limit the potential for reusing this carrier within the cellular communication system. For example, it is known to use frequency hopping techniques in order to provide statistically enhanced carrier reuse. However, with the broadcast carriers fixed for each cell, these carriers are typically unavailable for reuse in the frequency hopping plan. In addition, the transmit power of the broadcast control channel requires substantial geographic spacing of cells reusing the associated broadcast carrier thus exacerbating the optimization problem particularly in the picocellular environment.
Thus there is a need for a wireless communication system overcoming the reuse limitations associated with broadcast control channels and associated broadcast carriers and thus providing increased capacity and more efficient resource utilization.